Self-supporting load bearing voltage grading resistors for a lightning arrester

ABSTRACT

A lightning arrester characterized by having a plurality of self-supporting, semi-annular shaped voltage grading resistors that are adapted to support the weight of spark gap assemblies which are electrically connected in parallel therewith.

United States Patent Stetson 1 June 20, 1972 [54] SELF SUPPORTING LOAD BEARING VOLTAGE GRADING RESISTORS FOR A LIGHTNING ARRESTER [72] Inventor: Earl W. Stetson, Pittsfield, Mass. [73] Assignee: General Electric Company [22] Filed: Jan. 11, 1971 [21 Appl. No.: 105,724

Related U.S. Application Data [63] Continuation of Ser. No. 813,501, April 4, 1969,

abandoned.

[52] U.S. Cl ..3l5/36, 315/46, 315/52, 315/56, 315/11, 317/67, 317/78 [5 I Int. Cl...'. ..II0lt 5/04 [58] Field ofSearch ..3l5/36, 46,52, 56,71; 317/67, 68, 78

iii/ill [56] References Cited UNITED STATES PATENTS 3,152,279 10/1964 Masare ..3l3/23I OTHER PUBLICATIONS Encyclopedia of Chemical Technology, 1964, Vol. 4, p. 819.

Primary Examiner-Roy Lake Assistant Examiner-Darwin R. Hostetter Attorney-Vale P. Myles, Frank L. Neuhauser and Oscar B. Waddell [57] ABSTRACT A lightning arrester characterized by having a plurality of selfsupporting, semi-annular shaped voltage grading resistors that are adapted to support the weight of spark gap assemblies which are electrically connected in parallel therewith,

3 Claims, 5 Drawing Figures SELF-SUPPORTINGLOAD BEARING VOLTAGE GRADING RESISTORS FOR A LIGHTNING ARRESTER This'application is a continuation of Ser. No. 813,501, filed 4-4-9 now abandoned.

This invention relates to lightning arresters and, more particularly, to an improved voltage grading resistor arrangement for a valve type lightningarrester.

In conventional. valve type lightning ar'resters, a block of nonlinear resistance valve material is electrically connected in series with a plurality of arc-discharging spark gaps that are stacked in a column in the arrester with the valve material. In order to control the sparkover voltage of the arrester, frequently in prior art devices a plurality of voltage grading resistors are shunt connected across the respective series connected spark gaps to establish a predetermined voltage on each gap as a function of the line to ground voltage of the arrester. It has become common practice in present-day arresters to make such voltage grading resistors in the form of rectangular bars or cylinders that are provided with electrical contacts at their opposite ends to enable the resistors to be electrically connected to terminals at the opposite ends of the respective spark gaps across which the resistors are shunt connected.

Several significant problems are presented by such prior art voltage grading resistor arrangements. One of the major problems is that the elongated rectangular or cylindrical grading resistors require a substantial amount of space between the spark gap assembly and the inner cylindrical insulating wall of the lightning arrester housing. This means that for a given rating of resistor, the outer housing must be made larger, or the spark gap assembly housing must be made smaller, in order to leave adequate space therebetween to accommodate the grading resistors. Both of these expedients hamper the designer's ability to provide an optimum size of lightning arrester for a given interrupting rating. A second problem encountered with such a voltage grading resistance arrangement is that a substantial amount of labor is required to install the respective resistors in operating position within an arrester housing. Another difl'iculty encountered with such voltage grading resistor arrangements is that it is frequently difiicult to properly vary the amount of grading resistance between individual spark gaps because often provision is made only to mount a signal resistor across a given gap or pair of gaps.

My invention is intended to overcome the foregoing problems and difficulties of prior art voltage grading arrangements for lightning arresters. In accordance with this invention, a multi-gap lightning arrester is provided with voltage grading resistors that are semi-annular in shape. In one embodiment of the invention a plurality of semi-annular grading resistors formed of nonlinear resistance valve material are stacked one upon another and superposed within the insulating housing of a lightning arrester on a block of nonlinear resistance valve material that forms part of the main discharge path of the arrester. Also, mounted within the arrester, above the main nonlinear resistance valve, is a plurality of spark gap assemblies supported respectively on contact plates that have their peripheral edge portions positioned between adjacent pairs of the grading resistors. Thus, the spark gap assemblies are partially surrounded by the semi-annular grading resistors to thereby provide a substantialspace saving within the insulating housing of the arrester and at the same time the entire weight of the spark gap assemblies is supported by the grading resistors rather than being mounted in such a manner that the weight of at least some of the spark gap assemblies must be borne by other spark gap assemblies.

A further important feature of the semi-annular, or segmented, grading resistors utilized in lightning ar'resters constructed pursuant to my invention is that the free volume within the arrester housing is increased and thus improves the capability of an arrester of limited size to discharge a high-current arc in the event of arrester failure. The increased volume restricts a rapid build up of pressure within the arrester housing when such an arc is discharged by the arrester by afiording additional pressure relief or absorption volume within the housing.

A primary object of the present invention is to provide a lightning arrester having novel voltage grading resistors that overcome the above-noted problems.

Another object of the invention is to provide a lightning arrester having self-supporting voltage grading resistors that afford a stable support means for supporting the weight of spark gap assemblies in the arrester in a vertical column thereby to prevent these assemblies from mechanically loading one another.

A further object of the invention is to provide a lightning arrester having voltage grading resistors that make optimum efficient use of component mounting space in a lightning arrester housing.

Still another object of the invention is to provide a voltage grading resistor that is characterized by having a unique shape which serves to facilitate manufacture of the resistors.

Yet another object of the invention is to provide a voltage grading resistor for lightning arresters that can be produced without inducing dangerous mechanical stresses into the resistor during its manufacture, and that can be thermally cycled and mechanically loaded during operating use without introducing damaging mechanical stresses into the resistor.

Other objects and advantages of the invention will become apparent from the following description and claims, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side elevation, partly in cross section, of a lightning arrester embodying voltage grading resistors and support means constructed pursuant to the present invention.

FIG. 2 is a side elevation view, partly in cross section, of a prior art lightning arrester illustrating one method now used for mounting voltage grading resistors in shunt relationship with spark gap assemblies in an arrester housing.

FIG. 3 is a perspective view of a lightning arrester voltage grading resistor constructed pursuant to the present invention.

FIG. 4 is a top elevation of a voltage grading resistor of the type illustrated in FIG. 3.

FIG. 5 is a side elevation, fragmentary view, partly in cross section, of a portion of the lightning arrester depicted in FIG. 1

lightning arrester 1 having an insulating housing 2 formed of any suitable ceramic well known in the art. The opposite ends of housing 2 are sealed respectively by metal end cap terminals 3 and 4. The interior of arrester 1 is sealed from the atmosphere 'by suitable gaskets, such as gasket 5, disposed between the ends of the insulating housing 2 and the terminals 3 and 4. During the manufacture of the arrester, the gaskets (5) are compressed under a predetermined load applied to the terminal plates 3 and 4, then the peripheral edge of the terminal plates are turned to lock them into position as shown around the lip of the housing 2 that is depicted in cross-section at the bottom of the arrester l. Mounted on a terminal plate 411 is a compression spring 6 that supports the operating components of the lightning arrester 1. Specifically, a block of nonlinear resistance valve material 7 is supported by a disc shaped metal plate 8 and in turn has superposed above it a second metal contact plate 9 on which a plurality of semi-annular voltage grading resistors 10, 11, and 12 are stacked in self supporting relation. Also supported on contact plate 9 is a spark gap assembly 13 with its lowermost terminal plate 14 in direct electrical and mechanical contact with the plate 9. The upper terminal 15 of spark gap assembly 13 is in electrical and mechanical contact with another contact plate 16 which has its peripheral edge portions disposed between the adjacent ends of voltage grading resistors 11 and 12.

A second spark gap assembly 17 is positioned on the upper surface of another contact support plate 16a in a manner that will be explained further below. lt will be understood by those skilled in the art that the remaining portion of the arrester housing 2 above the components 7 through 16, just described, will be occupied by additional spark gap assemblies and voltage grading resistors similar to the assemblies 13 and 17 and resistors 10 l2, and additional blocks of main nonlinear resistance valves, such as valve 7 may also be disposed in this Referring now to FIG. 1 of the drawing, there is shown a Q portion of the housing in a manner well known in the lightning arrester art to provide a given predetermined arrester interrupting rating. Thus, a discharge path is formed from the top terminal 3 of the arrester 1, through the series connected spark gap assemblies and the nonlinear valve 7, past compression spring 6 through a conductive strap 18, to terminal plate 4a and thence to terminal 4.

Use of the novel voltage grading, semi-annular resistors 10 l2 pursuant to the teaching of the invention provides a mechanically stable, self-supporting stack of arrester components, as illustrated in FIG. 1. In FIG. 2 of the drawing there is shown, for comparison purposes, one type of prior art lightning arrester construction in which there is illustrated a spark gap assembly 19 having a first voltage grading resistor 20 and a second voltage grading resistor 21 shunt connected therewith. As can been seen in FIG. 2, this conventional method of mounting voltage grading resistors in a lightning arrester housing is relatively expensive, compared with the present invention shown in FIG. 1, in that the resistors 20 and 21 must be electrically connected to the top and bottom terminal plates 22 and 23, respectively, of spark gap 19 as well as being electrically connected to an intermediate terminal means 24 which helps mechanically support the resistors 20 and 21 in mounted position. In addition to being relatively expensive to assemble, such an arrangement results in mechanical loading of the spark gap assemblies, such as assembly 20 because all of the spark gap assemblies and nonlinear resistance valve blocks 25 and 26 are superposed in the arrester housing and must support the full weight of all the components in the upper portion of this stack.

In order to more fully explain the advantages and operation of the present invention, reference is now made to FIGS. 3 of the drawing. In FIG. 3 there is shown a perspective view of one of the nonlinear resistance voltage grading resistors, such as resistor 10. In the preferred embodiment of the invention, resistor is semi-annular, having a segment removed therefrom which is approximately equal to 90 of its circumferential length, as best seen in FIG. 4 of the drawing. This construction serves to prevent mechanical stresses from being formed in the resistor 10 during its manufacture because thermal stresses that tend to develop during a necessary firing operation are relieved by the ability of the resistor 10 to expand circumferentially as contrasted with a complete ring type resistor which would retain firing stresses and be subject to breakage when mechanically loaded by stacking other resistors on it in the assembled arrester. It will be understood that in other embodiments of the invention the specific size of the opening in the annulus comprising the voltage grading resistors may vary; however, it has been found that in order to provide a desirable degree of mechanical stability when such resistors are stacked in their self-supporting arrangement within an arrester housing, such as housing 2, it is desirable to form the semi-annular portion of the resistors to encompass at least 200 of the circumference of the spark gap assemblies 13 which they are adapted to surround. A further important advantage of this form of grading resistor is that many such resistors can be placed simultaneously on a tray of given size because the ends of adjacent resistors can be positioned in the central portion of other resistors on the tray. During manufacturing operations in which trays full of such resistors must be placed in ovens of limited size to fire,such spaced-saving construction has been found to be very valuable.

As can be seen in FIG. 3 of the drawing, a continuous strip of conductive metal 27 is deposited on the top surface of the resistor 10 and in like manner, another strip of metal 28 (not illustrated in the drawing) is deposited on the bottom surface of the resistor 10. These strips 27, 28, may be deposited by any conventional flame-spraying process of the type well known to those skilled in the art. The strips of metal, 27 and 28, form electrical contacts for assuring uniform conductivity with adjacent resistors, or contact plates, in engagement with the resistor 10 in its stacked, self-supporting position, as illustrated in FIG. 1 of the drawing.

The self-supporting arrangement of resistors 11, 12 and 12a, as well as the spark gap assembly supporting function of these resistors, will now be described more fully with reference to FIG. 5 of the drawing. It will be understood that FIG. 5 is an enlarged view of a fragmentary portion of the lightning arrester 1 shown in FIG. 1, with the same parts being identified by like reference numerals in both FIGS. 1 and 5. Thus, disposed between semi-annular voltage grading resistors 11 and 12 are a pair of contact plates 16 and 16a and spark gap assembly 17 is directly supported by the plate 16a. A compression spring 29 positioned above spark assembly 17 between a second pair of contact plates 30 and 30a resiliently biases the spark gap assembly 17 downwardly to retain it in position within the surrounding voltage grading resistors 12 and 12a.

Pursuant to the invention, in order to uniformly distribute or grade the voltage across the respective gaps housed in the chambers 17a and 17b of spark gap assembly 17 one of the electrodes in spark gap chamber 17a (not shown) is connected to one end 31a, of coil 31 and one of the electrodes in arcing chamber 17b (not shown) is electrically connected to the other end of coil 31 (not shown). End 31a of coil 31 is positioned between the ends of semi-annular voltage grading resistors 12 and 12a in electrical contact with the metalized strips thereon. In a suitable conventional manner, such as that illustrated in U.S. Pat. No. 3,151,273 Stetson et al., issued Sept. 29, 1964, the other electrode in chamber 17a is electrically connected to the contact plate 30 and the other electrode in chamber 17b is electrically connected to contact plate 16a and, as can be seen in FIG. 5, these contact plates 16a and 30 have their peripheral edge portions disposed between the opposite ends, respectively, of voltage grading resistors 12 and 12a and the next adjacent grading resistors. Thus, the electrodes in arcing chambers 17a are shunt connected by voltage grading resistor 12a and the electrodes in arching chamber 17b are shunt connected by resistor 12. Also, it will be noted that the entire weight of spark gap assembly 17 is completely supported by contact plate 16a so it does not mechanically load the spark gap assembly 13 positioned directly beneath it in the stack. It will be understood that this stacking arrangement and series of electrical connections is repeated throughout the successive spark gap assemblies of the lightning arrester 1 as discussed above with reference to FIG. 1. It should also be appreciated that a significant advantage of my invention is that the voltage grading arrangement, or upsetting, of the plurality of series connected spark gap assemblies of a lightning arrester can be very closely regulated by interchanging one semi-annular voltage grading resistor for another to compensate for variations in the electrical characteristics of the respective resistors. Such interchanging of these resistors is facilitated by the fact that each of them is mechanically the same size and shape and no permanently soldered connections are necessary between the respective resistors 11, 12 and 12a and the contact plates 16, 16a, 30 and 300, or to the conductive coil lead 31a.

As can be clearly seen in FIG. 1, when the grading resistors are stacked in assembled position, as shown, the open segment in each resistor 10, 11, 12 etc. forms an open column that provides a large passageway for arrester failure arc-generated gases allowing them to expand in virtually unrestricted fashion to fill the entire free volume of the arrester, rather than being restricted within the grading resistor stack to cause a temporary buildup of potentially damaging gas pressure. Thus, the added volume for gas expansion afforded by these removed segments of each grading resistor serve to provide additional gas pressure absorption capability within the arrester housing, since the free volume in the arrester is thereby increased.

It will also be understood by those skilled in the art that in relatively large lightning arresters using the present invention, it may be desirable to mechanically support the stacked components of the arrester with relation to the side walls of housing 2 by posinoning insulating spacers (not shown) between the inner walls of housing 2 and the stack of self-supporting semi-annular resistors 10, 11, and 12. My invention is ideally suited for incorporating such supporting means because, as can be seen in FIG. 5, an insulated support member could be readily fixed to the circumferential surface of the contact support plate, such as plates 16 and 160, between the respective semi-annular voltage grading resistors 11 and 12.

Further modifications of the invention will be apparent to those skilled in the art and it is my intention to encompass all such modifications and improvements in the scope of the following claims.

Iclaim:

1. In a lightning arrester having an insulating housing and a multi-gap sparkgap assembly within said housing electrically connected in series between two terminals of the arrester, the improvement comprising a plurality of voltage grading nonlinear resistors each of which is formed as a segment of an annulus that is adapted to expand and contract circumferentially without developing areas of concentrated mechanical stress therein whereby each segment partially surrounds the sparkgap assembly, said resistors being stacked in the arrester in self-supporting relation between said sparkgap assembly and the insulating housing of the arrester, and being electrically connected in series relation, thereby to afford a grading circuit that is adapted to conduct grading current when normal operating voltage is applied across said first and second terminals, and a plurality of electrical conductors connected to shunt predetermined portions of the series circuit formed by said resistors across the respective gaps of said multi-gap sparkgap assembly thereby to grade the voltage across each of said gaps as a function of the voltage across said series circuit, each of said voltage grading resistors being formed to encompass at least 200 of the circumference of said sparkgap assembly, and all of said grading resistors and a plurality of nonlinear resistance valves being stacked in a single, self-supporting column.

2. The invention as defined in claim 1 wherein the upper and lower surfaces of each of said grading resistors is metal coated to afford electrical contact between the respective resistors when they are stacked in self-supporting relation, and wherein said nonlinear resistance valve bears the entire weight of all of said grading resistors and said sparkgap assembly.

3. The invention as defined in claim 1 wherein a majority of said voltage grading resistors is in substantial vertical alignment whereby the open segments in said resistors define an open column between the respective ends of said resistors, said column being efiective to allow arc-generated gases developed in the sparkgap assembly to expand through it in virtually unrestricted fashion.

It IF I! III l UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,671,800 Da June 20, 1972 Inventor(s) Earl W. Stetson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line H, change T- P9" to L-4-69 line 43,0hange "signal" to single Col. 3, line 63,change "space to space- Signed and sealed this 31st day of October 1972.

(SEAL) Attest:

EDWARD M.FLE'ICHER,JR. ROBERT GOTTSCHALK Atte'sting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,671,800 Dated June 20, 1972 Inventor(s) Earl W. Stetson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 63,change "spaceg; to space- Signed and sealed this 31st day of October 1972.

(SEAL) Attest:

EDWARD M.FLETGHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. In a lightning arrester having an insulating housing and a multi-gap sparkgap assembly within said housing electrically connected in series between two terminals of the arrester, the improvement comprising a plurality of voltage grading non-linear resistors each of which is formed as a segment of an annulus that is adapted to expand and contract circumferentially without developing areas of concentrated mechanical stress therein whereby each segment partially surrounds the sparkgap assembly, said resistors being stacked in the arrester in self-supporting relation between said sparkgap assembly and the insulating housing of the arrester, and being electrically connected in series relation, thereby to afford a grading circuit that is adapted to conduct grading current when normal operating voltage is applied across said first and second terminals, and a plurality of electrical conductors connected to shunt predetermined portions of the series circuit formed by said resistors across the respective gaps of said multi-gap sparkgap assembly thereby to grade the voltage across each of said gaps as a function of the voltage across said series circuit, each of said voltage grading resistors being formed to encompass at least 200* of the circumference of said sparkgap assembly, and all of said grading resistors and a plurality of nonlinear resistance valves being stacked in a single, self-supporting column.
 2. The invention as defined in claim 1 wherein the upper and lower surfaces of each of said grading resistors is metal coated to afford electrical contact between the respective resistors when they are stacked in self-supporting relation, and wherein said nonlinear resistance valve bears the entire weight of all of said grading resistors and said sparkgap assembly.
 3. The invention as defined in claim 1 wherein a majority of said voltage grading resistors is in substantial vertical alignment whereby the open segments in said resistors define an open column between the respective ends of said resistors, said column being effective to allow arc-generated gases developed in the sparkgap assembly to expand through it in virtually unrestricted fashion. 